{
  "bibcode": "2008GCN..7420....1B",
  "body": "S. D. Barthelmy (GSFC), D. N. Burrows (PSU), J. Cummings (GSFC/UMBC),\nN. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD),\nK. L. Page (U Leicester), D. Palmer (LANL)\n\nAfter analysis of the data from the Swift BAT and XRT instruments, the \nSwift team is unable to conclude whether or not trigger is a real but \nfaint burst or a statistical fluctuation.  The source is detected at 7.1 \nsigma in the BAT 15-50 keV energy band.  However, no bright source was \nfound in the XRT data.\n\nUsing the data set from T-239 to T+303 sec from recent telemetry \ndownlinks, we report further analysis of trigger 306323 (reported as GRB \n080315, Page, et al., GCN Circ. 7416).\n\nThe BAT ground-calculated position is\nRA, Dec = 155.124 +41.701 deg which is\n    RA(J2000)  =  10h 20m 29.8s\n    Dec(J2000) = +41d 42' 3.6\"\nwith an uncertainty of 3.3 arcmin, (radius, sys+stat, 90% containment).\nThe image significance at this location is 7.1 sigma. The partial coding \nwas 98%.\n\nThe mask-weighted light curve shows a a single smooth bump starting at \n~T-5 sec and and ending at ~T+65 sec.  It appears only in the 15-50 keV \nband. T90 (15-350 keV) is 65 +- 5 sec (estimated error including \nsystematics).\n\nThe time-averaged spectrum from T+0.0 to T+64.0 sec is best fit by a \nsimple power-law model.  The power law index of the time-averaged \nspectrum is 2.51 +- 0.59.  The fluence in the 15-150 keV band is 1.4 +- \n0.5 x 10-7 erg/cm2. The 1-sec peak photon flux measured from T+0.00 sec \nin the 15-150 keV band is 0.04 +- 0.01 ph/cm2/sec.  All the quoted \nerrors are at the 90% confidence level.\n\nIn 20 ks of XRT Photon Counting mode data, a weak source is detected \nwithin the BAT error circle at a count rate of (9.5 � 3.0) X 10-4 \ncount/s. The coordinates of this source are RA, Dec (J2000) = 155.0856, \n+41.6847, which is equivalent to\n    RA  =  10 20 20.55\n    Dec = +41 41 04.8\nwith an estimated uncertainty of 5 arcsec (90% containment). It is not\npossible to determine whether this source is fading because of the \nlimited statistics. With the exception of this source, the 3-sigma upper \nlimit within the BAT error circle is 5.9 X 10-4 count/s.\n\nIt is unusual, but not unprecedented for there to be no XRT detection of \na Swift source.  Among the BAT triggers of long GRBs with prompt slews, \nXRT sees a source approximately 97% of the time.  Given the XRT \nnon-detection and the faintness of the BAT source, we cannot tell \nwhether this trigger is a statistical fluctuation or a real burst.\n\nThe results of the batgrbproduct analysis are available at\nhttp://gcn.gsfc.nasa.gov/notices_s/306323/BA/",
  "circularId": 7420,
  "createdOn": 1205615542000,
  "email": "hans.a.krimm@nasa.gov",
  "subject": "Swift trigger 306323: Swift-BAT/XRT refined analysis",
  "submitter": "Hans Krimm at NASA-GSFC  <hans.a.krimm@nasa.gov>"
}